/Engine/Source/Runtime/Engine/Classes/Engine/NetDriver.h
Called when an actor is being unloaded during a seamless travel or do due level streaming The main point is that it calls the normal NotifyActorDestroyed to destroy the channel on the server but also removes the Actor reference, sets broken flag, and cleans up actor class references on clients.
virtual void NotifyActorLevelUnloaded ( [AActor](API\Runtime\Engine\GameFramework\AActor) * Actor )